In a conventional hydrogen-cooled turbine generator, a heated part such as a coil is cooled by hydrogen gas sealed in the machine, a seal ring is provided for preventing leakage of the hydrogen gas to the atmosphere through a shaft penetrating portion, and seal oil is supplied to the seal ring to seal the hydrogen gas.
In the conventional seal oil supply device of this type, a differential pressure between the oil supply pressure at which the oil is supplied to the seal ring and the gas pressure inside the machine is controlled by a differential pressure regulation valve, but the absolute pressure of the oil supply itself is not directly controlled (see Patent Document 1).